1. Field of the Invention
The present invention relates to a multicasting technological field of an internet broadcasting system, and more particularly to a multicasting relaying method to achieve a multicasting under a modem environment utilizing a digital subscriber line (xDSL) and a public switch telephone network (PSTN) and a recording mechanism that can read a program to achieve the aforementioned method with a computer.
2. Brief Description of the Prior Art
An xDSL is a new transmission technology to provide a high-speed data transmission by using an upper band, a unused frequency band of a general telephone network, still guaranteeing the use of a conventional plain old telephone service (POTS).
Basically, the frequency bandwidth (transmission capacity) and modulation technique of analog signals determine how fast digital signals can be transmitted to analog signals.
The xDSL technology is a method by which the digital transmission speed can be improved by enlarging an analog bandwidth of a telephone network to solve a problem of narrow bandwidth, a problem of the conventional telephone line. In theory, the telephone network can be used to transmit analog signals having a bandwidth greater than 4 KHz, which is a voice bandwidth. However, the higher the transmission speed gets, the shorter the transmission distance is. The quality of the telephone network should be good. Accordingly, a variety of transmission speeds and transmission techniques have been developed according to transmission distance and transmission speed applied fields.
The xDSL is a generic name applied for several types of digital subscriber line techniques, including: asymmetric digital subscriber line (ADSL); symmetric digital subscriber line (SDSL); high-bit-rate digital subscriber line (HDSL); rate adaptive asymmetric digital subscriber line (RADSL); very high-bit-rate digital subscriber line (VDSL) and the like, providing high-speed multi-media services such as video on demand (VoD), high-speed internet connection, remotely controlled education and video phone by using the conventional telephone line.
However, a centralized server providing internet broadcasting programs generally transmits multimedia data to all users' terminals connected thereto. A plurality of internet users are connected with an internet broadcasting server, which provides internet broadcasting programs, to receive and appreciate all the broadcasting data, for instance, various multimedia data like moving pictures and audio data. In other words, according to an internet broadcasting system that has been used up to now, all the users are to be connected with a central server having a large capacity of an internet broadcasting server regardless of the number thereof.
As the development of multimedia technologies has been accelerated, the data transmission capacity gets greater to frequently cause a bottleneck phenomenon of communications or break down of internet services.
Particularly, the competitiveness of internet broadcasting programs depends on the superiority in the quality of images and sound. An increase in the data transmission capacity is indispensable for securing a competitive edge. Therefore, in order to provide high quality internet broadcasting services, it is inevitable to improve the function and capacity of the server. However, it is impossible in reality to make an endless improvement in the function and capacity of the broadcasting systems to satisfy demands of many internet broadcasting viewers.
Besides, if a server is connected by a number of users at one time, it is almost impossible to allow another user to get connected with the server in spite of superiority in its function and capacity. Even if another user gets connected with the server, there may be a problem in that the data transmission speed becomes too slow to see quality broadcasting.
In general, a data transmission on the internet is made through TCP/IP (Transmission Control Protocol/Internet Protocol).
In order to carry out an internet broadcasting through TCP/IP or a user datagram protocol (UDP), an identical data must be transmitted to several terminals by repeating same as many numbers as the number of terminals.
In order to solve the aforementioned problem, ‘IP multicasting’ is used. The IP multicasting is an internet reference standard specifically set up for broadcasting multimedia data such as simultaneous visual images or audio sounds through the internet. In other words, the IP multicasting is an internet protocol to set a specific address range labeled ‘Class D’ as an internet standard established to broadcast on the internet multimedia data like moving pictures and audio data and to transmit data to all terminals having the same address that fall in the specific internet address range labeled ‘Class D’ when one of the terminals sharing the same address sends data only once.
However, if an internet router connected with the terminal does not support the IP multicasting, the IP multicasting can be used only in a local area network (LAN) with which the terminal is in connection. Particularly, a terminal gets connected with an internet server by passing through a plurality of internet routers. At this time, if any of the routers does not support the IP multicasting, a terminal cannot receive broadcasting data from the internet server.
Furthermore, since internet routers designed to support IP multicasting are not sufficiently distributed, the internet broadcasting cannot be made by using IP multicasting in actuality. Therefore, it is rare to provide broadcasting services on the internet by using the IP multicasting. The IP multicasting is applied only to the intranet system of some enterprises. At present, most of internet broadcasting servers utilize TCP/IP or UDP, instead of the IP multicasting, for a direct connection between servers and terminals to transmit and receive broadcasting data. However, in the broadcasting mechanism, it is very difficult to make an increase in the number of users who can get connected with the server because there will be an extremely high communication load on the server. In other words, if a great number of users get connected to an internet broadcasting server, there may be a communication overload causing problems such as poor accessibility, data loss, low communication speed, server breakdown and high cost for construction of a system since it is necessary to use a very high functional server.
In order to solve the aforementioned problems, there should be a method for providing a quality internet broadcast to a plurality of users without a bottleneck phenomenon by allowing data to be relayed from a connected terminal to other ones. Moreover, there should be a method for restricting the number of terminals that can be directly connected with a server to thereby continuously provide internet broadcasting without the server breakdown even when there are a great number of users demanding an internet connection at the same time.
Preferably, description will be made on a method for expanding such a multicasting data dispersion environment (LAN environment) into a modem environment out of communication networks utilizing the xDSL and the PSTN.
In general, when ADSL or PSTN is used, data will be conveyed to a final network connector through the following procedure: Contents Providing server (CP), Internet Data Center (IDC), Internet Communication Service Provider (ISP); ADSL server (B-RAS); Asynchronous Transfer Mode (ATM) switch; ADSL Service Mechanism (DSLAM); a plurality of users or Contents Providing server (CP); Networking Storing Mechanism (NAS); Public Switch Telephone Network (PSTN); modem; and user (refer to FIG. 5).
In case of ADSL and PSTN, a method for connecting a user is similar following the steps of B-RAS and NAS. Therefore, description will be made mainly with ASDL hereinafter.
Generally, a connection network of ADSL through DSLAM is a network installed by an ADSL service provider through an analysis on the number of service users, the quantity of transmitting data, the required cost and the like to provide services to process upload 1 Mbps and download 8 Mbps at the same time. However, ADSL services have been provided for upload 10˜60 Kbps and download 300 Kbps in actuality. Recently, there have emerged a few service providers that are partly operated with download 1 Mbps.
In the system thus described, approximately 1000˜2000 users utilize each DSLAM and, if a cable modem is used with services provided by Dreamline, Thrunet or Hanaro, a device that has the same function as a Cable Modem Terminal System (CMTS) is used for services like an internet connection. However, if the DSLAM does not support multicasting, it can receive a signal only by a unicasting method with a limitation in the simultaneous access that can be made only within a given upload and download allotment capacity.
In order to overcome such a limitation, an IP multicasting method by way of Peer-to-Peer (P-to-P) method of an IP multicasting technique is used as an attempt to increase the number of simultaneous connectors. It has been well-known that the aforementioned method is a system for increasing the number of simultaneous connectors by relaying broadcasting data as upload while a particular client is listening to the same broadcasting.
However, in the aforementioned multicasting technique using the P-to-P method, a network capacity for transmitting upload data is restricted to 600 K per DSLAM at present (approximately 1 M at some services). Supposed the upload data capacity were 600 Kbps and one client transmitted upload signals of 150 K, it can be well known that two clients' upload signals are tied into one packet and taken as upload data. However, if the network capacity assigned for upload data is taken into consideration (in other words, the data capacity is supposed as 600 K), the upload packet of 150 K can be transmitted only to 4 clients at an identical DSLAM in the P-to-P method at the same time. If simultaneous connectors actually perform such a packet transmission in the multicasting technique using the P-to-P method at the same DSLAM, it becomes impossible for the other service users of the same DSLAM to make an upload transmission, thereby resulting in a state where an ADSL connection becomes impossible to be made.
Besides, there are not only the technical limitations as such, but also theoretical limitations on the number of the simultaneous connectors. If a particular ADSL service provider is taken into account in reality, approximately 33 B-RAS accommodate ADSL services for about 17 billion users. At this time, assuming that only ASDL users may get a simultaneous connection with the same broadcasting program, it can be estimated that about 50,000 users are connected to each B-RAS. If about one thousand users are connected with each DSLAM, about 50 DSLAM may be installed for one B-RAS. Thus, if there are 33 B-RAS, it can be predicted that about 1,650 DSLAMs are in operation. When one DSLAM takes upload 150 K for each of 4 users, there may be a first receiver for each DSLAM and two receivers by 4 upload users, that is, 3 receivers if the 300 Kbps of broadcasting data is transmitted in the P-to-P method by utilization of the total system resource. It is a limited system that allows simultaneous connections for approximately 4,950 users. (where, each DSLAM upload capacity is 600 K.)
In other words, some developers have made efforts to get a network reduction effect by simultaneously transmitting upload 150 K of another user in the P-to-P method in combination with an initial upload 150 K of a user. In the aforementioned method, if each of two users utilizes 150 K, the maximum number of simultaneous multicasting system connectors for each DSLAM is 7 with an assumption that the upload limitation of each DSLAM is 2 Mbps. When it is taken into consideration that there are 33 B-RAS possessed by the largest ADSL service provider (Korea telecom), it can be predicted that there is a physical limitation that the number of simultaneous connectors cannot exceed 11,550 if only ADSL users make a simultaneous connection to the multicasting relay of a particular internet broadcasting organization. In case of some ADSL services, the upload data capacity is regarded as about 600 K to the maximum level, there is exposed an extreme limitation that only 4,950 users can be simultaneously connected by 300 K stream provided that the maximum number of simultaneous connectors for each DSLAM is 3 and the total number of B-RAS is 33. As a result, there is a barrier that prevents expansion of multicasting in the Internet broadcasting organizations.
Therefore, it is required to develop a method to perform multicasting data dispersing and processing operations under a modem environment utilizing xDSL and PSTN.